feat: add variables to fail command

Client.UnitTests/FailJobTest.cs

@@ -16,19 +16,22 @@ public async Task ShouldSendRequestAsExpected()
             // given
             const string errorMessage = "This job failed!";
             const int jobKey = 255;
+            const string variables = "{\"foo\":23}";
             var expectedRequest = new FailJobRequest
             {
                 JobKey = jobKey,
                 ErrorMessage = errorMessage,
                 Retries = 2,
-                RetryBackOff = 1562
+                RetryBackOff = 1562,
+                Variables = variables
             };
 
             // when
             await ZeebeClient.NewFailCommand(jobKey)
                 .Retries(2)
                 .ErrorMessage("This job failed!")
                 .RetryBackOff(TimeSpan.FromMilliseconds(1562.5))
+                .Variables(variables)
                 .Send();
 
             // then

Client/Api/Commands/IFailJobCommandStep1.cs

@@ -59,5 +59,13 @@ public interface IFailJobCommandStep2 : IFinalCommandWithRetryStep<IFailJobRespo
         ///     to the broker.
         /// </returns>
         IFailJobCommandStep2 RetryBackOff(TimeSpan retryBackOff);
+
+        /// <summary>
+        /// Set the variables to fail the job with.
+        /// </summary>
+        /// <param name="variables">the variables (JSON) as String.</param>
+        /// <returns>the builder for this command. Call <see cref="IFinalCommandStep{T}.Send"/> to complete the command and send it
+        ///     to the broker.
+        IFailJobCommandStep2 Variables(string variables);
     }
 }

Client/Impl/Commands/FailJobCommand.cs

@@ -59,6 +59,12 @@ public IFailJobCommandStep2 RetryBackOff(TimeSpan retryBackOff)
             return this;
         }
 
+        public IFailJobCommandStep2 Variables(string variables)
+        {
+            request.Variables = variables;
+            return this;
+        }
+
         public async Task<IFailJobResponse> Send(TimeSpan? timeout = null, CancellationToken token = default)
         {
             var asyncReply = gatewayClient.FailJobAsync(request, deadline: timeout?.FromUtcNow(), cancellationToken: token);